Electronic thermometer having a heated probe

Claim 2

In combination for determining the temperature of an object, covering means having heat conductive properties, first means disposed within the covering means and defining a first electrical resistance having characteristics variable in accordance with the temperature of the object, second means disposed within the covering means in electrically and thermally insulated realtionship to the first means and defining a second electrical resistance having characteristics variable in accordance with the temperature at positions on the covering means enveloping the object, third means disposed within the covering means and defining a third electrical resistance having characteristics variable in accordance with the temperature of the object, fourth means responsive to any variations in the relative characteristics of the second and third means from a particular relationship for heating the covering means at the positions enveloping the object in accordance with such variations to restore the relative characteristics of the second and third means to the particular relationship, and fifth means for measuring the characteristics of the first electrical resistance upon the restoration of the relative characteristics of the second and third means to the particular relationship.

Claim 3

The combination set forth in claim 1 wherein first electrical leads extend between the second and third means to provide for determinations in the relative characteristics of the second and third means and the fourth means include second electrical leads extending externally from the covering means for providing for the flow of electrical current through the covering means to heat the covering means.

Claim 4

The combinations set forth in claim 1 wherein the first and third means are interrelated to provide substantially proportional characteristics in accordance with the temperature of the object.

Claim 5

The combination set forth in claim 1 wherein the fourth means include a bridge circuit including the second and third electrical resistances and also include heating means for heating the second means and further include switching means responsive to the operation of the bridge circuit for producing an operation of the heating means in accordance with variations in the second and third means from the particular level.

Claim 6

The combination set forth in claim 4 wherein first electrical leads are disposed within the covering means to connect the second and third electrical resistances in the bridge circuit and wherein the fourth means include second electrical leads extending into the covering means for providing for the flow of electrical current through the covering means to heat the covering means.

Claim 7

The combination set forth in claim 4 wherein the first and third means are disposed on a first chip having heat conducting and electrical insulating properties and wherein the second means are disposed on a second chip having heat conducting and electrical insulating properties and wherein the second chip is further displaced from the covering means than the first chip and wherein means are provided for maintaining the first and second chips in heat insulating and electrical insulating relationships to each other.

Claim 8

The combination set forth in claim 6 wherein means are disposed between the second chip and the covering means at the positions enveloping the object to provide a conduction of heat between the second chip and the covering means at the positions enveloping the object.

Claim 9

The combination set forth in claim 7 wherein the heating means include a fourth electrical resistance and wherein the fourth electrical resistance is disposed on the second chip in interrelated relationship with the second means and wherein the heat conducting means disposed between the second means and the covering means envelopes the first and second chips and electrical leads extend between the second and third means to connect the second and third means in the bridge circuit.

Claim 10

In combination for determining the temperature of an object, covering means having heat conducting properties, the covering means being constructed to be disposed in butting relationship to the object at a particular position on the covering means, first resistance means disposed in contiguous relationship to the covering means and in heat conducting relationship to the covering means to provide an electrical resistance having a variable value dependent upon the temperature of the object, second resistance means disposed in spaced and in electrically insulated and heat insulated relationship to the first resistance means and in heat conductive relationship to the area enveloping the particular position on the covering means to provide an electrical resistance having a variable value dependent upon the temperature of the object, servo means responsive to differences of a first particular polarity in the variable values of the first and second resistance means for producing heat in the second resistance means to introduce heat to the covering means in the area enveloping the particular position and to vary the value of the second resistance means in accordance with the introduction of heat to the second resistance means, and measuring means responsive to the elemination of the differences of the first polarity in the variable values of the first and second resistance means for providing an indication of the variable value of the first resistance means.

Claim 11

In combination for determining the temperature of an object, covering means having heat conducting properties, the covering means being constructed to be disposed in butting relationship to the object at a particular position on the covering means, first resistance means disposed in contiguous relationship to the covering means and in heat conducting relationship to the covering means to provide an electrical resistance having a variable value dependent upon the temperature of the object, second resistance means disposed in spaced and in electrically insulated and heat insulated relationship to the first resistance means and in heat conductive relationship to the area enveloping the particular position on the covering means to provide an electrical resistance having a variable value dependent upon the temperature of the object, servo means responsive to differences of a first particular polarity in the variable values of the first and second resistance means for producing heat in the second resistance means to introduce heat to the covering means in the area enveloping the particular position and to vary the value of the second resistance means in accordance with the introduction of heat to the second resistance means, and measuring means responsive to the elemination of the differences of the first polarity in the variable values of the first and second resistance means for providing an indication of the variable value of the first resistance means.

Claim 12

The combination set forth in claim 9 wherein first and second electrical leads are disposed within the covering means and are connected between the first and second resistance means and wherein the servo means include second electrical leads extending into the covering means from a position external to the covering means for providing an electrical current for producing heat in the second resistance means.

Claim 13

In the combination set forth in claim 9, means enveloping the first and second resistance means and having heat conducting properties for conducting heat from the second resistance means to the covering means in the area enveloping the particular posItion in accordance with the introduction of heat to the second resistance means.

Claim 14

In the combination set forth in claim 11, means disposed between the first and second resistance means within the heat conducting enveloping means for providing a heat barrier between the first and second resistance means and the atmosphere.

Claim 15

In the combination set forth in claim 9, the measuring means including a bridge circuit having feedback means and including the first resistance means in the bridge circuit for providing a first indication for unbalances in the bridge circuit of a first polarity and for providing a second indication distinctively different from the first indication for unbalances in the bridge circuit of a second polarity opposite to the first polarity.

Claim 16

In the combination set forth in claim 13, means disposed between the first and second resistance means for maintaining the first and second resistance means in heat insulating and electrical insulating relationships to each other, and means enveloping the first and second resistance means and having heat conducting properties for conducting heat from the second resistance means to the covering means in the area enveloping the particular position in accordance with the introduction of heat to the second resistance means, first means having heat conducting properties and disposed within the heat conducting enveloping means and supporting the first resistance means in contiguous relationship to the covering means, and second means having heat conducting properties and disposed within the heat conducting enveloping means and supporting the second resistance means in displaced relationship to the convering means.

Claim 17

In the combination set forth in claim 14, the covering means including a probe and a sheath removably disposed on the probe.

Claim 18

In combination for determining the temperature of an object, covering means having heat conducting properties, the covering means being constructed to engage the object at a particular position on the covering means, a first electrical resistance disposed in heat conducting relationship to the covering means at the particular position on the covering means, a second electrical resistance disposed in displaced relationship to the particular position on the covering means and to the first electrical resistance, first means disposed between the first and second electrical resistances to maintain the first and second electrical resistances in heat insulating and electrical insulating relationships to each other, and second means extending between the second electrical resistance and an area of the covering means enveloping the particular position on the covering means and having heat conducting properties and means providing for the introduction of heat to the second means to maintain the area of the covering means enveloping the particular position on the covering means at the temperature of the second electrical resistance.

Claim 19

In combination for determining the temperature of an object, covering means having heat conducting properties, the covering means being constructed to engage the object at a particular position on the covering means, a first electrical resistance disposed in heat conducting relationship to the covering means at the particular position on the covering means, a second electrical resistance disposed in displaced relationship to the particular position on the covering means and to the first electrical resistance, first means disposed between the first and second electrical resistances to maintain the first and second electrical resistances in heat insulating and electrical insulating relationships to each other, and second means extending between the second electrical resistance and an area of the covering means enveloping the particular position on the covering means and having heat conducting properties and means providing for the introduction of heat to the second means to maintain the area of the covering means enveloping the particular position on the covering means at the temperature of the second electrical resistance.

Claim 20

In the combination set forth in claim 16, the second means being constructed to envelope the first and second electrical resistances to provide a heat barrier between the first and second electrical resistances and the covering means except at the positions at which the first electrical resistance is disposed in heat conducting relationship to the particular position on the covering means and at which the second means is disposed in heat conducting relationship to the area of the covering means enveloping the particular position on the covering means.

Claim 21

In the combination set forth in claim 17, third means supporting the first electrical resistance within the second means in contiguous relationship to the particular position on the covering means and having heat conducting properties to provide a transfer of heat between the first electrical resistance and the particular position on the covering means, and fourth means supporting the second electrical resiStance within the second means in displaced relationship to the particular position on the covering means and having heat conducting properties, the first means being disposed between the third means and the fourth means to maintain the third and fourth means in heat insulating and electrical insulating relationship to each other.

Claim 22

In the combination set forth in claim 18, the covering means including a probe and a sheath removably disposed on the probe.

Claim 23

In the combination set forth in claim 18, a third electrical resistance supported by the third means in interleaved relationship to the first electrical resistance to provide a temperature directly related to the temperature of the first electrical resistance.

Claim 24

The combination set forth in claim 20 wherein first electrical leads are disposed within the covering means and are connected between the second and third electrical resistances and wherein second electrical leads extend into the covering means from a position external to the covering means to provide for the flow of current to heat the second electrical resistance.

Claim 25

In the combination set forth in claim 20, a fourth electrical resistance supported by the fourth means in interleaved realtionship to the second electrical resistance to provide a temperature directly related to the temperature of the second electrical resistance.

Claim 26

In combination for determining the temperature of an object, covering means having heat conducting properties and disposed in heat conducting relationship to the object at a particular position on the covering means, a first electrical resistance disposed in heat conducting relationship to the particular position on the covering means and constructed to provide a resistance value variable in accordance with the temperature of the object, a second electrical resistance disposed in heat insulating relationship to the first electrical resistance and in heat conducting relationship to an area of the covering means enveloping the particular position, and means connecting the first and second resistances in a relationship to maintain the first and second resistances at the same temperature to provide the area of the covering means enveloping the particular position on the covering means at the same temperature as the particular position on the covering means.

Claim 27

In combination for determining the temperature of an object, covering means having heat conducting properties and disposed in heat conducting relationship to the object at a particular position on the covering means, a first electrical resistance disposed in heat conducting relationship to the particular position on the covering means and constructed to provide a resistance value variable in accordance with the temperature of the object, a second electrical resistance disposed in heat insulating relationship to the first electrical resistance and in heat conducting relationship to an area of the covering means enveloping the particular position, and means connecting the first and second resistances in a relationship to maintain the first and second resistances at the same temperature to provide the area of the covering means enveloping the particular position on the covering means at the same temperature as the particular position on the covering means.

Claim 28

The combination set forth in claim 23 wherein the connecting means include electrical leads connected between the first and second electrical resistances and disposed within the covering means.

Claim 29

In a combination as set forth in claim 23 means disposed between the second electrical resistance and the area of the covering means eveloping the particular position on the covering means to provide for the passage of heat from the second electrical resistance substantially only to the area of the covering means enveloping the particular position on the covering means.

Claim 30

In a combination as set forth in claim 23 first positioning means disposed between the first and second electrical resistances to maintain the first and second electrical resistances in heat insulating and electrical insulating relationships to each other, and second positioning means enveloping the first and second electrical resistances and the first positioning means to provide a heat barrier between the atmosphere and the first and second electrical resistances and the first positioning means and disposed between the second electrical resistance and the area of the covering means enveloping the particular position on the sheath to provide a flow of heat between the second electrical resistance and the area of the covering means enveloping the particular position on the covering means.

Claim 31

In the combination set forth in claim 26, the covering means including a probe and a sheath made from a heat conducting material and removably disposed on the probe.

Claim 32

In the combination set forth in claim 27, tHe first positioning means constituting a first flat chip having heat conducting properties and the second positioning means constituting a second flat ship having heat conducting properties and the means disposed between the second electrical resistance and the area of the covering means enveloping the particular position on the covering means constituting an annulus.

Claim 33

In combination for sensing the temperature of an object, a probe body having a forward end and a rearward end, the forward end being positionable in proximity to the object; a sheath having heat conductive properties and disposed to cover at least the forward end of the probe body, the sheath having first portions constructed to be placed in contiguous relationship with the object and second portions enveloping the first portions; first means disposed at the forward end of the probe body in heat conductive relationship with the first portions of the sheath and having heat conductive and electrical insulating properties which cause the temperature of the first means to vary with the temperature of the first portions of the sheath; a first resistance member disposed on the first means and provided with electrical properties which vary with the temperature of the first means; second means disposed in the probe body rearwardly of the first means, the second means having heat conductive properties, a second resistance member disposed on the second means and provided with electrical properties which vary with the temperature of the second means; third means having heat insulating properties and disposed between the first means and the second means for maintaining the first means and the second means in heat insulative relationship; fourth means responsive to the differences in the electrical properties of the first resistance member and the second resistance member for producing heat in the second means and the second resistance member in accordance with differences in such electrical properties from a particular relationship to maintain such particular relationship; fifth means disposed between the second means and the second portions of the sheath for conducting heat between the second means and the second portions of the sheath in accordance with the heat produced in the second means and the second resistance member by the fourth means; and sixth means disposed between the fifth means and the first means for maintaining the fifth means and the first means in heat and electrical insulative relationship.

Claim 34

In combination for sensing the temperature of an object, a probe body having a forward end and a rearward end, the forward end being positionable in proximity to the object; a sheath having heat conductive properties and disposed to cover at least the forward end of the probe body, the sheath having first portions constructed to be placed in contiguous relationship with the object and second portions enveloping the first portions; first means disposed at the forward end of the probe body in heat conductive relationship with the first portions of the sheath and having heat conductive and electrical insulating properties which cause the temperature of the first means to vary with the temperature of the first portions of the sheath; a first resistance member disposed on the first means and provided with electrical properties which vary with the temperature of the first means; second means disposed in the probe body rearwardly of the first means, the second means having heat conductive properties, a second resistance member disposed on the second means and provided with electrical properties which vary with the temperature of the second means; third means having heat insulating properties and disposed between the first means and the second means for maintaining the first means and the second means in heat insulative relationship; fourth means responsive to the differences in the electrical properties of the first resistance member and the second resistance member for producing heat in the second means and the second resistance member in accordance with differences in such electrical properties from a particular relationship to maintain such particular relationship; fifth means disposed between the second means and the second portions of the sheath for conducting heat between the second means and the second portions of the sheath in accordance with the heat produced in the second means and the second resistance member by the fourth means; and sixth means disposed between the fifth means and the first means for maintaining the fifth means and the first means in heat and electrical insulative relationship.

Claim 35

The combination recited in claim 29 wherein the first means comprises: a backing having a thin and flat configuration and wherein the first resistance member is disposed as a thin coating resistance on the flat configuration of the backing member.

Claim 36

The combination recited in claim 30 wherein the second means comprises a backing having a thin and flat configuration and wherein the second resistance member is disposed as a thin coating on the flat configuration of the second means; and wherein the fourth means includes a bridge circuit including the first and second resistance members for producing heat in the second means and the second resistance member in accordance with particular unbalances in the bridge to maintain the second means at the temperature of the first means.

Claim 37

The combination recited in claim 31 wherein the bridge circuit is responsive to the resistance of the first resistance member and the resistance of the second resistance member to provide an output signal when the resistance of the second resistance member is less than the resistance of the first resistance member, and wherein a third resistance member is disposed on the second means as a thin coating in heat conductive relationship with the second means and is responsive to the output signal of the bridge network to pass an electrical current for heating the second means when the temperature of the second resistance member is less than the temperature of the first resistance member.

Claim 38

The combination set forth in claim 32 wherein the bridge circuit includes electrical leads disposed within the covering means and extending between the first and second electrical resistances and wherein second electrical leads extend into the covering means from a position external to the covering means to provide for the passage of electrical current to the third resistance member to heat the second means.

Claim 39

In combination for measuring the temperature of an object, a probe body having a forward end and a rearward end, the forward end being positionable in proximity to the object; first means disposed in proximity to the forward end of the probe body, the first means being provided with heat conducting properties and being disposed in heat conductive relationship with the object so that the temperature of the first means is substantially equal to the temperature of the object; a first temperature-sensitive resistor disposed on the first means and having an electrical resistance dependent upon the temperature of the first means; a second temperature-sensitive resistor disposed on the first means and having an electrical resistance dependent upon the temperature of the first means; second means provided with heat conducting properties and disposed rearwardly of the first means and in heat conductive relationship with positions on the probe body enveloping the forward end of the probe body and in heat insulative relationship with the first means; a third temperature sensitive resistor disposed on the second means and having an electrical resistance dependent upon the temperature of the second means; an electrical network responsive to the relative electrical resistances of the second temperature-sensitive resistor and the third temperature-sensitive resistor to provide a second output signal with particular characteristics dependent upon such relative electrical resistances; control means responsive to the second output signal for heating the second means and the third temperature-sensitive resistor to maintain the temperature of the second means at the temperature of the first means and the first and second temperature-sensitive resistors; and a first bridge network responsive to the electrical resistance of the first temperature-sensitive resistor upon the heating of the second means and the third temperature-sensitive resistor to the temperature of the first means and the first and second temperature-sensitive resistors to provide a first output signal indicative of the temperature of the first means.

Claim 40

In combination for measuring the temperature of an object, a probe body having a forward end and a rearward end, the forward end being positionable in proximity to the object; first means disposed in proximity to the forward end of the probe body, the first means being provided with heat conducting properties and being disposed in heat conductive relationship with the object so that the temperature of the first means is substantially equal to the temperature of the object; a first temperature-sensitive resistor disposed on the first means and having an electrical resistance dependent upon the temperature of the first means; a second temperature-sensitive resistor disposed on the first means and having an electrical resistance dependent upon the temperature of the first means; second means provided with heat conducting properties and disposed rearwardly of the first means and in heat conductive relationship with positions on the probe body enveloping the forward end of the probe body and in heat insulative relationship with the first means; a third temperature sensitive resistor disposed on the second means and having an electrical resistance dependent upon the temperature of the second means; an electrical network responsive to the relative electrical resistances of the second temperature-sensitive resistor and the third temperature-sensitive resistor to provide a second output signal with particular characteristics dependent upon such relative electrical resistances; control means responsive to the second output signal for heating the second means and the third temperature-sensitive resistor to maintain the temperature of the second means at the temperature of the first means and the first and second temperature-sensitive resistors; and a first bridge network responsive to the electrical resistance of the first temperature-sensitive resistor upon the heating of the second means and the third temperature-sensitive resistor to the temperature of the first means and the first and second temperature-sensitive resistors to provide a first output signal indicative of the temperature of the first means.

Claim 41

The combination set forth in claim 34 wherein first electrical leads are disposed within the probe body and are connected between the second and third temperature sensitive resistors and are included in the electrical network to provide for the production of the second output signal and wherein second electrical leads extend into the probe body from a position external to the probe body to provide for the passage of electrical current for heating the second means and the third temperature sensitive resistor.

Claim 42

The combination set forth in claim 35 wherein the bridge network includes first electrical leads disposed within the probe body and connected between the first and second temperature-sensitive resistors and second electrical leads extending into the probe body from a position external to the probe body and connected to the third temperature-sensitive resistor for providing for the passage of current through the third temperature-sensitive resistor to heat the third temperature-sensitive resistor.

Claim 43

The combination recited in claim 34 wherein fourth and fifth resistors and switching means are connected in a second bridge circuit with the second and third temperature-sensitive resistors and the switching means are responsive to the relative values of the second and third temperature-sensitive resistors in the brIdge circuit for controlling the passage of electrical current for heating the second means and the third temperature-sensitive resistor to the temperature of the first means and the first and second temperature-sensitive resistors.

Claim 44

A probe assembly for measuring the temperature of an object comprising: a probe body positionable at a first position in close proximity to the object at a first position on the object and having second positions enveloping the first positions; first means mounted in the probe body and providing a first heat conductive path from the first position on the probe body so that the first means has substantially the temperature of the first position on the object; second means mounted in the probe body, the second means providing a second heat conductive path to the second position on the probe body so that the second position on the probe body has substantially the temperature of the second means; third means for maintaining the first means and the second means in a heat insulative relationship; fourth means disposed in heat conductive relationship with the first means and having variable characteristics dependent upon the temperature of the first means; fifth means disposed in heat conductive relationship with the second means and having variable characteristics dependent upon the temperature of the second means; sixth means disposed in heat conductive relationship with the second means and responsive to the differences in the variable characteristics of the fourth means and the fifth means for heating the second means when the temperature of the first means is greater than the temperature of the second means; and seventh means responsive to the production by the sixth means of equal temperatures on the first and second means for measuring the temperature of the first means.

Claim 45

A probe assembly for measuring the temperature of an object comprising: a probe body positionable at a first position in close proximity to the object at a first position on the object and having second positions enveloping the first positions; first means mounted in the probe body and providing a first heat conductive path from the first position on the probe body so that the first means has substantially the temperature of the first position on the object; second means mounted in the probe body, the second means providing a second heat conductive path to the second position on the probe body so that the second position on the probe body has substantially the temperature of the second means; third means for maintaining the first means and the second means in a heat insulative relationship; fourth means disposed in heat conductive relationship with the first means and having variable characteristics dependent upon the temperature of the first means; fifth means disposed in heat conductive relationship with the second means and having variable characteristics dependent upon the temperature of the second means; sixth means disposed in heat conductive relationship with the second means and responsive to the differences in the variable characteristics of the fourth means and the fifth means for heating the second means when the temperature of the first means is greater than the temperature of the second means; and seventh means responsive to the production by the sixth means of equal temperatures on the first and second means for measuring the temperature of the first means.

Claim 46

The combination set forth in claim 38 wherein the fourth and fifth means respectively constitute electrical resistances having variable resistance values in accordance with their temperature.

Claim 47

The combination recited in claim 39 wherein the sixth means includes bridge circuit means including the fourth and fifth means for producing an electrical current to heat the second and fifth means upon unbalances in the bridge circuit means indicative of a lower temperature for the second means than for the first means.

Claim 48

The combination set forth in claim 38 wherein the first and second means respectively constitute chips having heat conducting properties and having flat faces and wherein the fourth and fifth means respectively constitute thin coatings disposed on the flat faces of the first and second means and provided with resistance values variable in accordance with their temperature.

Claim 49

The combination set forth in claim 38 wherein the second means includes a member having heat conducting properties and extending between the fourth means and the second positions on the probe body and enveloping the first, third, fourth and fifth means to provide a heat barrier between the first, second, third and fourth means and the atmosphere.

Claim 50

The combination set forth in claim 42 wherein the fourth and fifth means respectively constitute electrical resistances having variable resistance values in accordance with their temperatures and wherein the seventh means include bridge circuit means and further include the fourth means in the bridge circuit means and further include feedback means for providing a first indication for unbalances of a first polarity in the bridge circuit means and for providing a second indication distinctively different from the first indication for unbalances in the bridge circuit means of a second polarity opposite to the first polarity.

Claim 51

A probe assembly for measuring the temperature of an object, comprising: a probe body having a forward and a rearward end, the forward end being positionable in proximity to the object; a first backing member disposeD in proximity to the forward end of the probe body in heat conductive relationship with the object; a second backing member disposed rearwardly of the first backing member and having heat conducting properties; first means for maintaining the first backing member and the second backing member in heat insulative relationship; a first temperature-sensitive resistor disposed on the first backing member and having a resistance dependent upon the temperature of the first backing member; a second temperature-sensitive resistor disposed on the second backing member and having a resistance dependent upon the temperature of the second backing member; second means coupled to the first temperature-sensitive resistor and the second temperature-sensitive resistor and responsive to the resistance values of these resistors for heating the second backing member when the resistances of the first and second temperature-sensitive resistors have values indicating that the temperature of the second backing member is less than the temperature of the first backing member; third means disposed between the second backing member and the probe body at positions enveloping the forward end of the probe body for heating the area enveloping the forward end of the probe body to the temperature of the second backing member; and fourth means responsive to the production of resistance values for the second temperature-sensitive resistor indicative of equal temperatures in the first and second backing members for measuring the temperature of the first backing member.

Claim 52

A probe assembly for measuring the temperature of an object, comprising: a probe body having a forward and a rearward end, the forward end being positionable in proximity to the object; a first backing member disposeD in proximity to the forward end of the probe body in heat conductive relationship with the object; a second backing member disposed rearwardly of the first backing member and having heat conducting properties; first means for maintaining the first backing member and the second backing member in heat insulative relationship; a first temperature-sensitive resistor disposed on the first backing member and having a resistance dependent upon the temperature of the first backing member; a second temperature-sensitive resistor disposed on the second backing member and having a resistance dependent upon the temperature of the second backing member; second means coupled to the first temperature-sensitive resistor and the second temperature-sensitive resistor and responsive to the resistance values of these resistors for heating the second backing member when the resistances of the first and second temperature-sensitive resistors have values indicating that the temperature of the second backing member is less than the temperature of the first backing member; third means disposed between the second backing member and the probe body at positions enveloping the forward end of the probe body for heating the area enveloping the forward end of the probe body to the temperature of the second backing member; and fourth means responsive to the production of resistance values for the second temperature-sensitive resistor indicative of equal temperatures in the first and second backing members for measuring the temperature of the first backing member.

Claim 53

The probe assembly recited in claim 44 further comprising: a relatively short wire connected from the first temperature-sensitive resistor to the second temperature-sensitive resistor; and relatively long conductors extending from the heating means to control the operation of the heating means.

Claim 54

The probe assembly recited in claim 44 wherein the heating means includes: a bridge network responsive to the resistance of the first temperature-sensitive resistor and the resistance of the second temperature-sensitive resistor for providing an output signal when the temperature of the second backing member as represented by the resistance of the second temperature-sensitive resistor is less than the temperature of the first backing member as represented by the resistance of the first temperature-sensitive resistor; and a third temperature-sensitive resistor disposed on the second backing member and responsive to the output signal of the bridge network for heating the second backing member until the temperature of the second backing member as represented by the resistance of the second temperature-sensitive resistor is substantially equal to the temperature of the first backing member as represented by the resistance of the first temperature-sensitive resistor.